Copper alloy for electronic material used for various electronic components such as connector, switch, relay, pin, terminal, leadframe and so forth is basically required to satisfy both of high strength and high electro-conductivity (or heat conductivity). With recent accelerated progress in higher integration, downsizing and thinning of electronic components, more advanced levels of requirement have been directed to the copper alloy used for components of electronic instruments. In particular, the copper alloy used for floating connector and so forth has come to be used under larger current. In order to prevent dimensional expansion of the connector, the copper alloy necessarily has a good bend formability even if thickened (0.3 mm or more), an electro-conductivity of 60% (65) IACS or larger, and a 0.2% yield strength of approximately 650 MPa or larger.
Cu—Ni—Si alloy, generally referred to as Corson-series alloy, is a representative copper alloy showing relatively large electro-conductivity, strength and bend formability. This sort of copper alloy is improved in the strength and electro-conductivity, by allowing fine Ni—Si intermetallic compound grains to deposit in a copper matrix. It is, however, difficult for the Cu—Ni—Si alloy to achieve an electro-conductivity of 60% IACS or larger, while keeping a desirable strength. Under the circumstances, Cu—Co—Si alloy is now gathering attention. The Cu—Co—Si alloy is advantageously adjustable to show larger electro-conductivity than the Cu—Ni—Si alloy, by virtue of its lower solid solubility of cobalt silicide (Co2 Si).
Processes largely affective to characteristics of the Cu—Co—Si alloy include solution treatment, aging and finish rolling, among which the aging is one of the process most affective to distribution or grain size of deposits of cobalt silicide.
Patent Literature 1 (JP-A-09-20943) describes a Cu—Co—Si alloy which is developed aiming at higher strength, higher electro-conductivity and larger bend formability. A method of manufacturing the copper alloy described herein is such as including hot rolling, subsequent cold rolling with a reduction of 85% or more, annealing at 450 to 480° C. for 5 to 30 minutes, cold rolling with a reduction of 30% or less, and aging at 450 to 500° C. for 30 to 120 minutes.
Patent Literature 2 (JP-A-2008-56977) describes compositions of copper alloys, as well as a Cu—Co—Si alloy designed while taking size and total content of inclusions possibly appear in the copper alloy into account. Also described is a method which includes solution treatment, and subsequent aging at 400° C. or above and 600° C. or below, for 2 hours or longer and 8 hours or shorter.
Patent Literature 3 (JP-A-2009-242814) describes a Cu—Co—Si alloy introduced as a precipitation-hardened copper alloy material, expected to stably achieve a high level of electro-conductivity of 50% TAGS or above which is hardly achieved by the Cu—Ni—Si alloy. The literature also describes a method including steps of facing, subsequent aging at 400 to 800° C. for 5 seconds to 20 hours, cold rolling with a reduction of 50 to 98%, solution treatment at 900° C. to 1050° C., and aging at 400 to 650° C., taking place in this order.
Patent Literature 4 (WO2009-096546) describes a Cu—Co—Si alloy characterized in that size of deposit containing both of Co and Si is 5 to 50 nm. The literature also describes that aging after solution recrystallization is preferably conducted at 450 to 600° C. for 1 to 4 hours.
Patent Literature 5 (WO2009-116649) describes a Cu—Co—Si alloy excellent in strength, electro-conductivity, and bend formability. Examples of the literature describe the aging at 525° C. for 120 minutes, rate of heating from room temperature up to the maximum temperature fallen in the range from 3 to 25° C./min, and a rate cooling in furnace, down to 300° C., of 1 to 2° C./min.
Patent Literature 6 (WO2010-016428) describes a Cu—Co—Si alloy successfully improved in strength, electro-conductivity, and bend formability, by adjusting a value of Co/Si to 3.5 to 4.0. The literature also describes that the aging after recrystallization is proceeded at 400 to 600° C. for 30 to 300 minutes (at 525° C. for 2 hours in Example), the heating rate is adjusted to 3 to 25K/min, and the cooling rate is adjusted to 1 to 2K/min. The bend formability is evaluated by 90° W-bending test at R/t=0 and 180°-bending test at R/t=0.5, wherein samples are rated as “good” if bendable at least either in good way (GW) or bad way (BW). The rating, however, includes the case where the samples are rated as “good” in GW, but rated as “bad” in BW, only with a limited accuracy of evaluation for R/t. Moreover, the evaluation is only available up to a thickness as small as 0.2 mm, but not available at a thickness as thick as 0.3 mm.